This invention relates to blocking incoming telephone calls and specifically to an apparatus and method for allowing only a predetermined set of telephone numbers to complete a telephone call thereby blocking access to numbers not within the predetermined set.
Caller identification is a popular service provided by telephone communications service providers. In accordance with caller identification service, a subscriber or called party is provided the telephone number (by in-band signaling means) of a calling party. In conjunction with subscribing to this service the calling party""s number is displayed either on separate device, a caller identification device or box, or a telephone at the called party""s location. Caller identification devices have evolved from their initial primitive state to be more sophisticated devices that provide memory for storing telephone numbers. The numbers that are stored in memory are usually a set of numbers to whom the called party wishes to deny call completion. These stored numbers therefore form a set of calling numbers that are rejected as part of the caller identification service. The stored numbers then provide a call rejection service in conjunction with the caller identification service. Of course call rejection via this service or method works perfectly provided the subscriber populates the memory with the numbers except for only those from which a call is desired (a daunting task despite the fact that memory is relatively cheap). On the other hand, the called party, if present when the phone rings, may simply look at a telephone number display on the caller identification box and determine whether to answer the call. Accordingly, the called party may choose not to answer a call based on the calling party""s number.
Of course, the calling party can block the transmittal of its number by dialing a pre-specified code which gives an indication of xe2x80x9cNo Number Deliveredxe2x80x9d at the called party""s location. In such situations, the called party may choose to have the call automatically terminated, usually after one ring, as part of the caller identification service. On the other hand, and as described in Hashimoto""s U.S. Pat. No. 5,341,411, (hereinafter Hashimoto) the called party can manually bypass or override the automatic rejection of calls from the calling party whose number is not sent or is stored in the caller identification device or box. By Hashimoto""s method, even where the calling party""s number is blocked the called party may still be able to manually screen the call by playing an answering machine message and allowing the calling party to leave their number. Hashimoto provides this additional improvement on caller identification service by way of a more sophisticated caller identification device that initiates an answering machine based on underlying ringing voltages that occur before the service provider can terminate the call.
In U.S. Pat. No. 5,781,613, Knuth, et. al., (hereinafter Knuth) improve on Hashimoto by seizing a blocked calling party""s number after one ring and relaying an appropriate message to the calling party. Again, as ashimoto, Knuth requires human intelligence to decide whether the caller should be responded to (note here that in the context of this invention a message to the effect that xe2x80x9cBlocked calls are not acceptedxe2x80x9d is not considered a response). Most notably, neither Knuth nor Hashimoto restricts access to the called party based on a set of authorized users or phone numbers. That is, the called party is always successful in completing the call.
In contrast, limiting phone line access to a predetermined set of numbers is a rather desirable feature for the public telephone companies, public utilities, universities, businesses, and, to a certain extent, consumers. With respect to telephone companies, the loss of man power over the years has resulted in a substantial increase in the remote monitoring of many office functions such as the power systems, alarm control systems, environmental control systems, etc. Remote monitoring also provides the cost advantage of is reducing craft personnel having to service offices and remote sites. More than likely remote monitoring is done through the Public Switched Telephone Network (PSTN) over a phone line terminating on a modem. Many other public utilities, e.g., power companies, also monitor different aspects of their respective networks over the PSTN. In general, utilities, telephone service providers, universities and businesses all have computer systems which are accessible by dial-in phone lines over the PSTN. The use of public telephone lines to remotely monitor telephone equipments, environmental control systems, or computer systems has certain associated security risks. Most prominent is the risk that hackers will somehow access this mission critical equipment and cause damage to the equipment or its operation thereby resulting in economic or human harm. For the telephone service provider, unauthorized access to the PSTN""s power, alarm, and control monitoring systems could lead to significant loss of revenue. With respect to consumers, the ability to eliminate unwanted telemarketing-calls is rather enticing. More importantly, as homes become smarter, consumers will be able to purchase smart systems that are accessible via a modem over the PSTN. As such, consumers will be subject to ever increasing exposure to invasion of their privacy and homes, albeit electronic invasion. Physical security provides the foremost insurance against intrusion or theft.
Popular methods of restricting access to computer systems include providing a database of authorized telephone numbers on the very computer system that includes the protected information. In one prior art method the computer resource to which access is requested queries the calling party for a PIN. In another method the computer resource accepts the call, hangs up, and dials back the calling party provided the number matches one stored in a database. In yet another prior art method, the computer resource checks the number against a list residing in the computer""s memory. All these systems suffer from the drawback that the telephone call is established prior to determining whether the calling party is an authorized party.
In U.S. Pat. No. 5,901,284, Hamdy-Swink (hereinafter Hamdy-Swink) describes a method for restricting access to a called party before establishing the telephone call. The Hamdy-Swink method and system are, however, rather sophisticated and costly. To begin, Hamdy-Swink requires use of the Advanced Intelligent Network (AIN) to implement the security methods described therein. The AIN requires the use of costly switching systems and rather complicated software to operate. In addition, Hamdy-Swink authenticates the user based on the exchange of a security token. Essentially, Hamdy-Swink uses the PSTN to provide security by authenticating the user prior to establishing the end-to-end telephone connection. Accordingly, this method is not intended for the user who does not want a costly network based or private solution.
Accordingly, a device or system that filters telephone calls based on the telephone number would be desirable for the public telephone companies, utilities, and consumers. Filtering the phone call and allowing access to only those authorized are intended as a security enhancement over the firewall or other more sophisticated forms of computer security. Such a system should be simple and fairly inexpensive, both to purchase and to maintain. Furthermore, it would also be desirable if such a system is not network based or a unique private solution.
Our invention is an electronic security system that prevents incoming calls from all but a small set of originating caller phone numbers from reaching a called party""s telephone, modem, or computer. Our system is available to any user of the PSTN that needs to restrict incoming caller access to a specific telephone or modem circuit, provided such user is willing to subscribe to the caller identification service. With the system in place, only pre-authorized calling phone numbers can complete a call to the protected line. At the heart of our invention is a device or apparatus that can be implemented with relatively few inexpensive components. When the device is coupled to a commercially available caller identification device in accordance with one aspect of our invention, only a predetermined set of telephone numbers are accessible to either a destination modem or a telephone set.
It is therefore an object of our invention to secure the called party""s subtending equipment, most likely a computer system, against hackers by not establishing the telephone call unless the calling party""s number is among a list of authorized numbers.
It also an object of the present invention to secure a called party""s subtending equipment for relatively minimal cost and without the need for complex computer systems.
Accordingly, our system includes a connection circuit coupled to the public switched network to which is also coupled a caller-ID signal decoder;
a caller-ID number comparator is also coupled to both the caller-ID signal decoder and the connection circuit. The connection circuit is finally coupled to the secured modem or computer system and an off hook detector.
In an aspect of our invention, upon reception of an incoming call, the connection circuit holds the telephone line open, i.e., the line is kept on-hook. The caller-ID signal decoder then decodes the in-band message having the telephone number of the calling party. The decoded telephone number is then fed to the comparator which sends out a release signal to the connection circuit upon finding a telephone number in memory that matches the calling party""s telephone number. The connection circuit, responsive to the release signal, then allows the call through by coupling the ringing voltage to the called party""s subtending equipment. An off hook detector is thereafter used to sense the end of the call previously established in accordance with our invention. Once the off hook detector senses the end of the call, it resets the connection circuit.
In accordance with another aspect of our invention, if the caller identification device is replaced with a controller having memory and a processor other features can be implemented including time of day call blocking, dynamic number management, and password access.